This invention relates to the control of agricultural implements and in particular to implement arrangements which due to their size or complexity are difficult to control manually. As used herein, the term "implement" refers to an overall earth working mechanism, such as a plough, while the term "tool" refers to an individual earth working device, such as a plough share, mounted on an implement. For example, larger implements (such as long ploughs) are often mounted at one position (typically the front end of the implement) on a tractor vehicle via a movable implement support linkage and are supported at another position (typically the rear or center region of the implement) on a wheel or other ground engaging means.
Conventionally, such implements are controlled manually by the tractor operator who adjusts the position of the support linkage and wheel by visual inspection in order to maintain the implement at the required height and attitude. Each adjustment of depth made on the support linkage must be followed very quickly by an adjustment of the depth of the support wheel. Operation of such implements thus requires considerable skill and high levels of concentration make their use tiring, particularly bearing in mind the relatively complex maneuvering required each time the implement (for example, a plough) is lowered or raised at the beginning and end of each pass along the field in order to obtain a minimum length of headland.